For a number of years it has been known to provide a so-called "mother" board for supporting a plurality of circuit cards. Such a mother board is typically made in accordance with printed circuit techniques and contains a number of layers of circuitry. This is to say, by initially creating several discrete layers of circuit paths, interleaving them with bonding material, and then securing these layers together by the application of heat and pressure, a mother board of comparatively rigid material can be created.
The printed circuit cards supported on the mother board are each equipped with a large number of pins which are inserted into the mother board, with the arrangement being such that certain circuit portions on each card are connected to desired portions of the mother board, with the mother board having flexible appendages so as to ultimately connect certain cards to power supplies, discrete components, and the like.
It is necessary on the mother board to provide hole patterns to receive the pins of the numerous cards used thereon, and as is obvious, an appropriate electrical connection must be made between each received pin and the appropriate layer of the mother board. That this may be accomplished, the industry has for some years now utilized plated through holes in the mother board, and as is obvious, the plating must be sufficiently complete as to assure appropriate circuitry connections to each layer of the mother board to which continuity is required.
In order to assure the proper plating of the numerous holes appearing in the mother board, it is customary to work with the mother board having complete copper faces on both exterior portions, so that electrical continuity can be provided to each hole during the electroplating procedure. It is also typical to either move the board back and forth while suspended in the electrolytic material, or else agitate the fluid in a certain way so as to assure that each of the numerous holes of the mother board will be properly plated throughout its interior. Then, after the holes have been properly plated, the undesired portions of the copper faces on the exterior of the mother board are etched away so as to leave the desired hole portions.
Inasmuch as wiring harnesses made up of discrete wires is bulky as well as expensive, the industry, for a number of years now, has used flat conductor cables that are sufficiently flexible as to allow installation of the mother board in missiles and the like in which space is at a premium, which cables must conform to whatever paths are available between different portions of the missile. Typically, these flat conductor cables are also made by printed circuit techniques in which the circuit paths are encapsulated to prevent undesired shorting.
The flexible conductor cables were connected to the mother board at appropriate locations by the use of terminal pins, soldered joints, and the like, but in each instance in which these various techniques were used, many problems arose causing improper connections with the corresponding loss of continuity. In addition, much hand labor was involved, resulting in slow and expensive production.
Efforts in accordance with prior art teachings to create flexible appendages integral with a multilayer board, if indeed such were previously ever attempted, were doomed to failure because of the inability, prior to the present invention, of providing plated through holes not only in the mother board, but also in the termination portions of the flexible appendages, where connections were to be made to input and output devices, power supplies, discrete components, and the like. This statement is made because the flexible appendages, by their very nature, tend to undertake undesirable movements during the plating procedure, that are inconsistent with the proper plating of the holes therein.